Hb Saint Nazaire (beta 103[G5]Phe-->Ile): a new example of polycythemia due to a hemoglobin variant with increased oxygen affinity

Hb Heathrow [β103(G5)Phe→Leu], a First Report in an Asian Patient with Erythrocytosis

Congenital erythrocytosis (CE) is a rare and heterogeneous disease. The high oxygen affinity hemoglobin (Hb) variants are the most common cause of CE. Herein, we report a Korean patient with isolated erythrocytosis. A 25-year-old man was referred to our hospital for evaluation of high Hb level (Hb 20.4 g/dL, hematocrit 58%, reticulocyte count 2.90%, white blood cell count 6.83×10⁹/L, and platelet count 195×10⁹/L). Bone marrow biopsy revealed normocellular marrow without myeloproliferative features. JAK2 (V617F, exon 12), CALR (exon 9), and MPL W515K/L mutations were not detected. P₅₀ (partial pressure at which Hb is half saturated with oxygen), which is an indicator of left-shift of oxygen dissociation curve (high oxygen affinity state), was 14.3 mm Hg (reference value 22.6-29.4 mm Hg). He was suspected to have CE. Mutation analysis of the HBB gene revealed the known Hb variant, Hb Heathrow [β103(G5)Phe→Leu]. This is the first report of Hb Heathrow in Asian.

High oxygen affinity hemoglobins

High oxygen affinity hemoglobins are responsible for rare and heterogeneous autosomic dominant genetic diseases. They cause pure erythrocytosis, sometimes accountable for hyperviscosity and thrombosis, or hemolysis. Differential diagnoses must be first ruled out. The diagnosis is based on the identification of a decreased P50, and their possible characterization by cation exchange-high performance liquid chromatography and capillary electrophoresis. Finally, genetic studies of the responsible globin chain gene will confirm the mutation. The prognosis mainly relies on the P50 decrease rate and on the hemoglobin cooperativity impairment. Disease management should be personalized, and it should primarily depend on smoking cessation and physical activity. Phlebotomy and platelet aggregation inhibitors' prescriptions can be discussed. There is no contraindication to flights, high-altitude conditions, or pregnancy. Nevertheless, blood donation must be prohibited.

A novel hemoglobin variant found on the α1 chain: Hb KSVGH (HBA1: p.Lys57_Gly58insSerHisGlySerAlaGlnValLys)

Glycosylated hemoglobin (Hb A1C) is a crucial indicator for the long-term control and the diagnosis of diabetes. However, the presence of hemoglobin (Hb) variants may affect the measured value of Hb A1C and result in an abnormal graph trend and inconsistency between the clinical blood sugar test and Hb A1C values. In this study, laboratory data of 41,267 patients with diabetes were collected. The Hb A1C levels and the graph results were examined. We identified 74 cases containing abnormal Hb A1C graph trends. The conducted blood cell counts and capillary Hb electrophoresis were used to analyze Hb variants. We also determined gene variation for the Hb variants by a sequence approach. Fifteen different types of Hb variants were identified in this study. Among these, we found a novel variant in which the α1 subunit of Hb showed an insertion of 24 nucleotides (nts) between the 56th and 57th residues. We named this novel variant Hb Kaohsiung Veterans General Hospital (Hb KSVGH) (HBA1: p.Lys57_Gly58insSerHisGlySerAlaGlnValLys).

Hemoglobin Debrousse (beta 96[FG3]Leu-->Pro): a new unstable hemoglobin with twofold increased oxygen affinity

Hemoglobin Debrousse (beta 96[FG3]Leu-->Pro) is a new unstable variant, with high oxygen affinity responsible, in the steady state, for an apparently well-compensated chronic hemolytic anemia. The functional properties of this variant are due to the replacement of a leucine residue which is involved in the hydrophobic environment of the proximal side of the heme. This electrophoretically neutral hemoglobin was found as a de novo case in a 6-year-old girl suffering from severe anemia with hemolysis and transient aplastic crisis, following infection by parvovirus B19.